U.S. Pat. No. 5,928,512 to Hatch et al. illustrates and describes two embodiments of personal filtration devices for mounting on a bottleneck (11) of a flexible thin walled plastic bottle (12). U.S. Pat. No. '512's FIGS. 1 and 2 show a personal filtration device (10) for deployment inside a bottleneck (11), and including a filter element (14) in the form of a porous tubular cylindrical block of activated carbon particles. U.S. Pat. No. '512's FIGS. 3 and 4 show a personal filtration device (41) for externally extending from a bottleneck (11), and including a pre-filter element (60) consisting primarily of a particulate media bed (61), and a pleated paper filter element (66) for serially filtering contaminated water. The personal filtration devices (10) and (41) have threaded connector means for screw threading onto a bottleneck (11) (see U.S. Pat. No. '512, Col. 5, lines 3 to 5, and lines 36 to 39). The personal filtration devices (10) and (41) have an end cap (37) with a manually operated open-closed slide valve (40) (see U.S. '512, Col. 5, lines 10 to 13). However, the aforesaid personal filtration devices do not have arrangements for hermetically sealing their filter arrangements, thereby shortening their lifetimes due to contact with water contents, and airborne free radicals. Moreover, the aforesaid personal filtration devices are intended for screw thread mounting on bottlenecks with specific external thread dimensions. But standard bottleneck sizes do not exist, thereby precluding the aforesaid personal filtration devices for use with other bottles than their intended ones.